1. Field of the Invention
The present invention relates to a robot for transfer of glass, and more particularly, to a robot for transfer of glass that prevents stains and defects caused by a robot hand.
2. Discussion of the Related Art
Liquid Crystal Display (LCD) devices have become widely used due to advantageous characteristics such as compact size, thin profile, and low power consumption. As such, LCDs have become substitutes for Cathode Ray Tube (CRT) displays.
In general, the LCD device includes an LCD panel, wherein the LCD panel includes a thin film transistor substrate, a color filter substrate, and a liquid crystal layer. The thin film transistor includes a gate line, a data line, a thin film transistor, and a pixel electrode. The gate line crosses the data line at the right angle, thereby defining a pixel region. The thin film transistor and the pixel electrode are formed in the pixel region. The color filter substrate generally includes a color filter layer and a common electrode. The liquid crystal layer is formed between the thin film transistor substrate and the color filter substrate.
A method for fabricating the LCD device generally includes three processes: a substrate fabrication process, a cell process, and a module process.
The substrate fabrication process includes two steps of forming a thin film transistor array and forming a color filter array. In the step of forming the thin film transistor array, a plurality of thin film transistors and pixel electrodes are formed on a lower substrate. In the step of forming the color filter array, a color filter layer of R, G and B is formed on an upper substrate having a black matrix layer by using pigment or dye, and a common electrode of ITO is formed on the upper substrate.
During the cell process, spacers are formed between the lower substrate having the thin film transistor array and the upper substrate having the color filter array, to maintain a cell gap between them. Then, the two substrates are bonded to each other, and liquid crystal is injected between the two substrates, thereby forming an LCD panel having a plurality of cells.
In the module process, the LCD panel is connected with a signal processing circuit to form an LCD device.
To fabricate the LCD device through the substrate fabrication process, the cell process and the module process, it is necessary to load the substrate into various equipment, or to unload the substrate from the equipment in order.
Also, since it is impossible to stop the fabrication process line due to some defects of the equipment, a plurality of substrates are moved together using a cassette for temporarily storing the substrates. Accordingly, the plurality of substrates are loaded into the cassette by a transfer robot and unloaded from the cassette by the transfer robot according to the predetermined order.
FIG. 1 is a perspective view of a transfer robot according to the related art.
As illustrated in FIG. 1, the transfer robot 50 according to the related art includes a main axis 51, a robot arm 52, and a hand part 53. The robot arm 52 is mounted on the main axis 51 allowing it to rotate, wherein the robot arm 52 may also move in parallel, fold, or extend. The hand part 53 is provided in the fore end of the robot arm 52, wherein the substrate 15 is loaded on the hand part 53.
In the transfer robot 50 having the aforementioned structure, the substrate 15 is unloaded from the cassette (not shown) by the robot arm 52. Then, the substrate 15 is loaded on the hand part 53, and the substrate 15 is loaded on a stage 25 by rotation of the hand part 53. The stage 25 is positioned on an opposite side to the cassette (not shown). A plurality of lift pins 26 are provided in the stage 25, wherein the lift pins 26 move up and down. If the substrate is positioned on the stage 25 by the rotation of the robot arm 52, the lift pins 26 are moved upward, whereby the substrate 15 is separated from the robot arm 52. After separating the substrate 15 from the robot arm 52, the lift pins 26 are moved downward so that the substrate 15 is loaded onto the stage 25.
When the substrate 15 is stored in the cassette, the substrate 15 may be oriented at a slant or may be straight. Accordingly, the robot 50 senses and compensates for the position and orientation of substrate 15 (X-axis, θ-axis, the traveling axis) when loading the substrate 15, whereby the substrate 15 is loaded on the stage 25 at the correct position.
Referring to FIG. 1, the X-axis is defined along the direction of motion for forwarding the substrate toward the stage 25. The θ-axis is defined by the rotation to make substrate 15 and the stage 25 in parallel when the plane surface of the substrate 15 is otherwise diagonal to the plane surface of the stage 25. The traveling axis is defined as the direction of translation along the θ-axis, and may be orthogonal to the X-axis. Motion along the traveling axis is for aligning the substrate 15 with the stage 25 when the substrate 15 is positioned at the side of the stage 25.
To sense the position of the substrate 15, the hand part 53 of the transfer robot 50 has first and second sensors 54 and 55. The first and second sensors 54 and 55 sense the position state of the substrate 15. For example, the first and second sensors 54 and 55 detect the position of the substrate 15 relative to the X-axis and θ-axis. Accordingly, the transfer robot 50 senses the correct position of the substrate 15, and aligns the substrate 15 according to a compensation value, and then loads the substrate 15 on the stage 25.
FIG. 2 illustrates a hand part 53 of a related art robot for transferring a substrate. As illustrated in FIG. 2, the hand part 53 is provided with a connector 34, a plurality of plates 38, and a plurality of pads 39. One side of the connector 34 is connected with the robot arm 52 of FIG. 1. The plurality of plates 38 are arranged along one direction at fixed intervals at the other side of the connector 34. The plurality of pads 39 protrude from the upper surface of each of the plates 38. The plurality of pads 39 are formed of rubber to fix the substrate 15 by a vacuum force.
The related art robot for transferring a substrate has the hand part 53, wherein the hand part 53 is provided at the fore end of the robot arm 52 so that it can be rotated, translated, and extended. Also, the hand part 53 has the plurality of pads 39, wherein each of the plurality of pads 39 includes a ring-shaped sidewall for fixing the loaded substrate.
FIG. 3 illustrates the pad 39 of FIG. 2. As illustrated in FIG. 3, each of the pads 39 is formed of a main body having a circle-shaped bottom. The pad 39 includes a sidewall 41 and a bottom 42. A hole 43 of the predetermined diameter is formed in the center of the bottom 42. Although not shown, the vacuum device is additionally provided to supply the vacuum force to the pad 39.
When the substrate 15 is loaded on the hand part 53, the vacuum force is provided to the pad 39, whereby the substrate 15 is fixed to the pad 39. Then, the substrate 15 is transferred to the next process.
However, the robot for transferring substrates according to the related art has the following disadvantages.
When the substrate is in contact with the pads 39 after a baking process of 200° C. or more, an amount of heat from the substrate is conducted to the pad 39, causing a localized temperature drop on the substrate. Accordingly, the contact efficiency is lowered on the portions of the substrate having the temperature drop. After etching the substrate after a development process, the portions of the substrate subject to the temperature drop may have the various defects such as an adhesion failure in the respective layers of array, rolling, and thermal images.
Especially, as the substrate has the thin profile, an amount of heat is easily transmitted from the surface of the substrate to the pad 39. Thus, the yield may be lowered due to the defects such as a thermal image.
Accordingly, as the substrate is fixed to the pad by the vacuum force, ring-shaped prints are formed on the substrate due to the sidewall of the pad. The ring-shaped prints of the substrate may cause a thermal image along with the mechanical deformation due to thermal expansion and contraction.
In addition, stains may be generated on the substrate due to the use of pads. Especially, when loading the substrate spin-coated with a conductive material, stains can be generated on the substrate, thereby lowering the yield.